Your startup idea may be great, but what ends up making it a success may be a little different or a lot different.
A key part of the Agile methodology is to fail fast. What this means is, learn from mistakes quickly. Failing fast means measuring results, and continuously adapting until the results are better. It means listening to your customers, making changes to try things in different ways until you hit the mother lode. Instead of being a gold miner, you might end up making shovels or gold pans, and having a steady, profitable business.